drawVideoBackground() kills my text engine?

Hello from germany :)

I have some problems using different text engines to draw text in openGL ES 2.0 with the vuforia SDK with Android (Java). I know the different approaches (texture atlas, generate bitmap, ...), but none of the different engines seems to work for me...

Now I'm using the textengine from this site: http://androidblog.reindustries.com/a-real-opengl-es-2-0-2d-tutorial-part-8-rendering-text/

When everything in the renderFrame() function is commented out, it works perfect:

void renderFrame()
    {
        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);
        //Create a new Textmanager (tm) with default text
        SetupText();
        
        if(tm!=null)
			tm.Draw(mtrxProjectionAndView,0);
}

But as soon as I uncomment the drawVideoBackground() function, it doesn't render correctly:

void renderFrame()
    {
        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);

        State state = Renderer.getInstance().begin();
        
        //no more text, just black fields
        Renderer.getInstance().drawVideoBackground();
        
        //Create a new Textmanager (tm) with default text
        SetupText();
        
        if(tm!=null)
			tm.Draw(mtrxProjectionAndView,0);

        Renderer.getInstance().end();
}

It looks the same if I comment out the drawVideoBackground() call and enable GL_DEPTH_TEST. But with the drawVideo call it makes no difference whether GL_DEPTH_TEST is activated or not. 

So I think, the text-engine is working, but something is weird, I'm missing something or so...

Thanks for your help,

Steffen